(1) Field of the Invention
This invention is related to image reader, in particular to the paper feeder of the image reader.
(2) Description of the Related Art
An image reader is usually used in a scanner, a copier, a facsimile machine, etc. All these equipment contain an image reader. To increase the throughput, automatic document feeders (ADF) are customarily used.
FIG. 1 shows such an ADF, including a feeding roller 162 for picking up a sheet of paper 10 to be scanned, a taking up roller 164 to take up the paper 10 after scanning, an upper guide plate 12; a left lower guide plate 142; a central lower guide plate 144; a right lower guide plate 146. The three lower guide plates and the upper guide plate 12 form a curved conduit for the paper to move and to read the image. The bottom of the central guide plate 133 is transparent and is used to read the image at the bottom of the paper 10.
An light ray 152 is incident on the bottom side of the paper and is reflected as a ray 154 to an image sensor 18 for image processing.
FIG. 2 shows another common practice. The paper feeding roller 162 , the take-up roller 164 and the upper paper guide 12 function in a similar way as in FIG. 1 for feeding the paper 10. However the lower paper guides 242, 244 and 246 form a unitary transparent arc.
Both the paper guides shown in FIG. 1 and FIG. 2 have a common drawback as shown in FIG. 3. Due to the finite distance between the upper paper guide 12 and the lower paper guide 144, the paper fed between these guides may wrap in the lateral direction orthogonal the direction of the paper feed. The warping may be due to warping of the paper, paper rubbing, air disturbance in the paper passage, or jittering of the rollers 162, 164 when the rollers are turn on and off.
FIG. 4 shows another cause of paper distortion when the paper 10 wrinkles along lines perpendicular to the direction of the paper movement between the upper guide plate 12 and the lower guide plate 144.
In FIG. 3 and FIG. 4, the image on the paper is read by means of the reflected light rays 1641, 1642 and 1643 incident on the image sensor 18, from which the image is processed. Due to paper, an original straight line on the image becomes crooked or distorted. Such a distorted reproduction is not satisfactory to high quality image reproduction.
High quality reproduction especially important for digital processing, such as pattern recognition, digital camera and digital drawings.
An object of this invention is to improve a paper feeder structure for high quality reproduction of a scanned paper. Another object of this invention is to avoid paper warping in a paper feeder.
These objects are achieved in this invention by putting pressure at the line where the incident light ray is reflected. By exerting pressure, the paper is flattened at the points of light incidence. The pressure may be exerted by a spring, a weight or a roller.